The invention disclosed herein relates to form-work. The invention is applicable to producing constructions using form-work from concrete and other curable non solid materials. In particular but without intending to limit the scope of the invention the invention herein is directed to the construction industry and applicable to forming constructs from concrete. The construction industry and forming concrete constructions will be used to illustrate the invention herein but it will be appreciated that this is for explanatory purposes only.
In the construction industry it is often desired to form a construct by erecting temporary form-work and pouring concrete within the form-work. Once the concrete has cured or set the form-work is removed. Structures such as walls, curbs, suspended slabs, ramps and stairs are examples of structures poured in situ.
Other structures, including buildings, are made of large concrete panels. These panels can be manufactured off site and transported to a building site or alternatively such panels can be poured on-site and once set raised and located in position.
Structures such as stairs can be made from concrete poured into a specifically built form-work. Typically, timber and plywood are used to make the form-work. The form-work is held together with nails and braced into place. It can take a significant length of time to build the form-work. Once the form-work has been used it is removed and most is discarded. Accordingly, there is the expense of materials and labor in constructing the form-work. Further the work-site can become littered with off-cuts of timber and nails posing a hazard to workmen.
In the manufacture of rectangular concrete construction panels there are a number of techniques used in the construction industry for this purposes. Such panels can be made on-site or off-site.
Panels made off-site should be made with at least two sets of lifting anchors. One set for loading onto a delivery vehicle and another for unloading and erecting in place. This is because most manufacturers of such anchors will guarantee their anchors for a single lifting operation. Since this requires extra anchors and transportation of heavy items panels are often made on-site. Off-site made panels are typically manufactured more accurately in terms of dimensional accuracy, conformity and squareness than on-site made panels.
In most on-site panel manufacturing process a number of panels are made in a stack of typically four or six panels each lying horizontal one on top of the other. These stacks are typically manufactured on a concrete work-site surface or floor. Each panel is poured in sequence. Once cured the panel is coated with a substance, commonly called Bond Breaker, to prevent subsequent concrete adhesion. Then a further panel is poured and the process repeated as desired. When ready each panel is lifted and erected vertically in place.
A first known system for panel manufacture is the shutter system. This system relies on pre-fabricated shutters made from typically plywood sheets and a timber frame to hold the sheets together. The shutters and frame are typically pre-fabricated on-site requiring cutting of sheets and timber, and nailing together the frame and shutters. Each sheet is nailed to a timber frame which typically goes about the perimeter of the sheet with intervening support timbers. The shutters are constructed high enough to accommodate manufacturing a stack of panels typically up to six high.
The panel size is marked out on the concrete work-site floor. The base of the frame of each shutter is fixed to the work-site floor by drilling holes, using concrete anchors, and bolting the frame to the floor. The shutters are then plumbed and fixed in place by nailing timber braces to the frame and to timber brace plates which are fixed using concrete anchors to the work-site floor.
Once the shutters or form-work is erected the desired panel thicknesses are marked on the form-work face. Then fillets are nailed to the form-work face at these thicknesses to mold a chambered panel edge. The accuracy of the panel thicknesses is dependant upon the accuracy of the marking out process. This process is subject to human error in reading a tape measure or a dumpy level and transposing the desired marks to the form-work sides.
Compounding the mentioned problems of inaccuracy of panel thickness is the nature in which concrete needs to be worked. The poured concrete needs to be screed. Generally form-work is made so that its topmost edge is the desired level of the concrete. Then the screeding tool is run along the edge of the form-work thereby working the concrete to the desired level. With the shutter system all but the last panel must be screed to a line rather than an edge which is for more difficult to achieve and often leads to variation is panel thickness.
Once the form work is constructed reinforcing rods and mesh are set up within the form-work as required by the panels. Since the form-work is that required for a full stack this means that installing the reinforcing rods and mesh is hindered by the form-work. Care must be used not to damage the form-work or injury to a workman as the reinforcement is carried over the edge of the form-work.
The pouring and working of concrete leads to lateral pressures being experienced by the form-work. This is especially so when a machine is used to vibrate and compact the concrete in place. As the timber bracing typically is temporary and inexpensive it will often move under the lateral pressures thereby moving out of plumb. Once a stack is out of plumb it is impossible or at least very difficult to re-plumb form-work without dismantling the form-work and re-assembling. Even when the form-work is dismantled and re-assembled it is very difficult to correctly set up the form-work plumb and square. The effect of the form-work being out of plumb is to change the dimensions of the panel including thickness.
It will be clear from the above that the shutter system is very labor intensive. The form-work is bulky, heavy and requires large quantities of materials. Further, the panel forming operation is hampered by the form-work.
Another known system is the timber edge board system. In this system timber boards or planks are used on edge to act as the side-form. The width of the timber planks are the same as the intended thickness of the panel.
Upon a concrete work-site surface the intended panel dimensions are marked out. Then timber supports are made and set out. The supports typically include a timber base, a timber riser and a brace between the riser and the base. The join between base and riser is generally strengthened by use of a steel angle plate nailed to the base and riser. The support is set back from the marked panel so that the riser is the thickness of the planks from the marked panel. In this position the support are fixed to the concrete surface by use of concrete anchors and bolts.
A number of supports are positioned about the marked out panel. Then planks are cut and nailed together to form the side-form of the panel. These joined planks are nailed to the risers of the supports and the whole frame work plumbed and squared. Fillet edges are nailed to the inside face of the side-form planks. Then the reinforcing rods and mesh are installed and the concrete poured and screed. Once the concrete is cured another set of side-form planks are fixed to the risers sitting on edge on the top edge of the planks of the first set of planks. The new side-form is plumbed and squared and the next panel is manufactured. The process is repeated until the desired number of panels in the stack is reached.
It will be appreciated that this system does not require the side-forms, the planks, to be of width to form many panels. Rather the width of the plank is that of the desired panel thickness. This permits the poured concrete to be conveniently screed to the top edge of the side-form excepting in the proximity of the risers. About the risers great care is needed not to damage the risers supporting the side-form. Also, the problems associated with transporting the reinforcing metal work into the form-work are much less than shutter system.
As each panel has its own side-form planks it is possible to level, plumb and square the form-work for each panel. In this manner the problems associated with lateral forces on the side-forms can be corrected. This process does however take some time and skill.
It will be appreciated from the above that each panel has its own side-forms which remain in situ until the stack is dismantled and the panels erected. Consequently the system is expensive in terms of requiring many side-form planks.
Given the need to minimize cost and also to provide flexibility and convenience of working, the planks are of rough sawn timber. Rough sawn timber is supplied in nominal sizes with a significant tolerance in dimensions. The width and thickness of such planks can vary by a few millimeters. This variation is transferred to the manufactured panels but is typically increased. For example, a rectangular panel manufactured using timber side-forms typically varying by up to 5 mm (0.2 in) can lead, since there are two parallel side-forms, to a panel varying in width by 10 mm (0.4 in) from that of the intended width.
Added to the above problem, is the effect weather and work-site environment can have on the timber plank. Such a plank can shrink, swell, twist or warp compounding the problems mentioned above.
A further problem associated with rough sawn timber, planed timber being uneconomic, is that it has a pronounced timber grain. This grain is molded into the concrete surface of the panel edges. Where visible, such as around a window, further work and materials are required to hide the grain imprinted surface.
A further known system is the TILT-FAST system. This system utilizes square cross-section, tubular steel frames which are stacked horizontally one on top of another to form a riser and buttress. The cross-sectional height of a frame is that of the desired panel thickness.
The frames are laid out on a concrete work-site surface and fixed thereto using concrete anchors. To the panel facing side of the frame of each riser is affixed horizontally on edge a plywood plank of width equal to that of the height of the frame. The plywood planks are affixed using a pin and wedge system. By using a level on the face of the plywood plank which becomes the side-form together with the pin and wedge fixing system the side-form can be plumbed. Once the side-forms are plumbed fillets are nailed in place at the top and bottom edges. Then the concrete can be poured and the panel screed and formed.
When the panel is cured the frames are unbolted from the work-surface and the side-forms pulled away from the panel. A frame is re-bolted in each riser position and another frame is secured on top of each frame so that each riser comprises two frames. The plywood planks, without the fillets, are re-secured to the upper most frame of each riser and re-plumbed. Then the fillets are re-nailed and the next panel is manufactured. This process is repeated until the desired number of panels in the stack is reached.
The required re-alignment of the frames after they are dismantled to permit removal of the side-form is a time consuming process. It can also damage the anchorage of the concrete anchor holding the frame to the floor.
The process of constantly nailing, de-nailing and re-nailing the fillets is time consuming and labor intensive. Further, the plywood plank are quickly damaged beyond usefulness.
Though the system uses relatively small and light components there are many of the components. There are all the frames, the wedges and the pins which must be arranged, aligned and fixed correctly otherwise variation in panel dimensions can result. Therefore the system is slow and requires care to use which has an associated labor cost.
The nature of the frames limits the system to use for manufacture of standardised panel thickness. Currently, the known standard sizes are 125 mm, 150 mm and 175 mm. Each panel thickness requires another set of frames. Further, the side-forms are known to be typically composed of 2.4 m (7.87 ft) lengths of 25 mm (1 in) thick plywood which requires joints for panels of dimension greater than that.
This system has a further problem associated with it that the other systems need not suffer from should a dumpy level or a laser level be used to layout the fillet lines. This problem is that the frames are fixed to the floor. Therefore should the floor not be level, which is the likely situation, then each panel will be twisted or distorted rather than rectangular in cross section through out its length as is desired.